The present invention relates generally to the field of gas ionization detectors, and more particularly to an integrated ΔE-E annular gas ionization detector.
Ion beam analysis (IBA) is a suite of analytical techniques in which a high energy ion beam is used to probe the near-surface layer of solids, such as thin films used in semiconductor fabrication, to obtain composition and, in some cases, depth profile information. Different IBA techniques are directed to varying the parameters of the beam, such as the beam energy and the incident angle of the beam with respect to the surface of the solid. The different analytical techniques may produce different interactions of the ion beam and the surface. Analyzing the interaction products may provide meaningful information about the surface layers of the solid.
One IBA technique known as Rutherford Backscattering Spectrometry (RBS) probes the surface of a target by detecting the energies of particles of the incident ion beam that are backscattered into a particle detector by atoms of the target. As is well known in the art, the energies of the backscattered particles are proportional to the mass and energy of the incident particles of the ion beam, the mass of the atoms from which the incident particles are backscattered, and the scattering angle.
With some of the IBA analytical techniques, for example, nuclear reaction analysis (NRA), the interaction of the ion beam with the surface layers may produce more than one type of particle. Distinguishing the particles may be done by determining their atomic numbers and their energies.
For measurement of the atomic number as well as the energy of energetic atoms and ions, a device commonly referred to as a ΔE-E telescope detector is often used. The ΔE-E detector includes a pair of detectors arranged so that the particles travel through a first ΔE detector and are stopped in a second E detector. The atomic number may be determined from the energy deposited by the particle within the thickness spanned by the ΔE detector, and in the E detector as the particle is stopped. The deposited energy depends on the atom number, the particle's incident energy, the gas type, and gas pressure. The total energy of the incident particle is the sum of the energy deposited in the two detectors, and energy not detected, or lost, when, for example, the particle passes through an electrically conductive window, such as a metalized Mylar film, when entering the detector, or through a dead layer in a silicon detector.
The deposited energy is typically converted into a detected electrical signal with a magnitude proportional to the deposited energy. How the deposited energy is converted into an electrical signal depends on the type of detector. Typically, almost all the energy deposited within the detectors is the result of exciting electrons of the detector material. In the case of a gas ionization detector the number of ion-electron pairs can be detected. In the case of solid detector materials, such as scintillators and semiconductors, the energy deposition typically leads to promotion of electrons across the band gap. This may cause photon emissions in the case of the scintillator, or a current pulse flowing across a junction in the case of a semiconductor detector.